Perhaps because he muddied the water even more from 1990 onwards. He may have been instructed to of course , to try and mislead the west about missile/rocket technology?
We have pretty good indication that the lights or UFO's in the sky can be explained, even by someone that is less connected or as inexperienced as Ivanov. Ivanov may not have understood the reported lights in the ski in 1959 but by 1990 and with his career, along with satellite and man going to the moon, I suspect he would have worked out the explanation for the sightings , or at least researched it and put it forth as a plausible explanation. But he seems to deliberately throw in some amateur speculation not comparable to his professional position and connection s. If he wasn't responsible and some author used his name , then ivanov didn't seem to try and correct anything.
That's my thoughts anyway.